The deep-pocketed Club for Growth PAC endorsed the opponents of Reps. Paul GosarPaul Anthony GosarQuiet jockeying for McCain seat angers Republicans Paul Ryan refutes rumors of early retirement from House The Senate must act on the House-passed appropriations bills MORE (R-Ariz.) and Mark Critz (D-Pa.), a sign they may spend heavily against the two House freshmen.

Gosar is facing a tough primary in a district that includes a lot of new territory. The Club is backing Arizona state Sen. Ron Gould (R) over him in the primary in the solidly Republican district. Also in the race is Pinal County Sheriff Paul Babeu (R), who has faced ongoing ethics questions.

The group also endorsed Tea Party favorite Keith Rothfus against Critz, who recently won a primary against fellow Rep. Jason Altmire (D-Pa.) but currently represents only a quarter of the district he's running in. Critz is completing his first full term after winning a special election in 2010 to succeed the late Rep. John Murtha (D).

Some Democrats have privately voiced concern that he could be vulnerable in the Republican-leaning district, which has more people in the Pittsburgh suburbs than in Critz's base in Johnstown, nearly two hours from the city. But Rothfus, who nearly beat Altmire in 2010, was not Republicans' top recruit for the race.

The Club for Growth usually focused on primary rather than general elections, making this an unusual endorsement. If it spends heavily on the race it could have a major impact.

The group also endorsed Tom Massie in the primary to replace retiring Rep. Geoff Davis (R-Ky.) in a heavily Republican district.

This post was updated at 3:20 p.m.